Using :hover is a smart idea! You might want to add an entry in RELEASE-NOTES.
Not the history table...! Just the main image please. The history should show tranparency regardles.
I don't necessarily agree with that (but really its a bikeshed)
A I've stated in the bug, if you have to hover over everyone of them, it is going to be very annoying (they're thumbs anyway). The history is to check for errors in one lookover. So history (and possibly images in categories) should have transparency turned on.
I'm tempted to repond to the situation Edokter sketched, but it's quite clear that there are a few issues to figure out before doing anything. Suggesting we elaborate further on BugZilla, where clearly the discussion wasn't over yet.
Reverted in r91761.